Infection from a spider bite causes Romana's personality to change. Meanwhile the Doctor, after discovering that the spaceship society is in a perpetual state of repair and upgrade, has morality issues with the ship's leading scientist who readies himself to perform gruesome experiments on the live marshchild while it's fully conscious.
| Name | Type | Role | |
|---|---|---|---|
| Andrew Smith | Writer | ||
| Barney Lawrence | Guest Star | ||
| Tony Calvin | Guest Star | ||
| Richard Willis | Guest Star | ||
| Andrew Forbes | Guest Star | ||
| George Baker | Guest Star | ||
| June Page | Guest Star | ||
| Norman Bacon | Guest Star | ||
| Bernard Padden | Guest Star | ||
| Peter Grimwade | Director |